In a non-volatile memory field, many studies have been conducted on especially flash memory and also ferroelectric memory (FeRAM), MRAM (Magnetic RAM), OUM (Ovonic Unified Memory), and the like.
In recent years, a Resistance Random Access Memory (ReRAM) different from these non-volatile memories has been proposed. Information can be written into ReRAM by setting a resistance value of a variable resistance layer of a memory cell by applying a voltage pulse and read out information without destruction. With respect to the ReRAM, the cell area is small and a multivalued memory can be realized. Therefore, it is recognized that there is a possibility that the ReRAM will have performance exceeding that of the existing non-volatile memory.
In a status in which it is absolutely necessary to process a great number of information, the ReRAM in which a large volume data can be read and written at low power consumption, high reliability, and high speed is needed. In order to realize this ReRAM, the various technologies are proposed for the variable resistance layer used for the ReRAM (patent document 1 and non-patent document 1).
In patent document 1, a non-volatile element using the variable resistance layer composed of a tantalum oxide layer and a transition metal oxide layer that is formed of a metal different from tantalum is disclosed. In non-patent document 1, the variable resistance element using a tantalum oxide layer having an oxygen concentration gradient across the layer from an interface with one electrode layer to an interface with the other electrode layer as the variable resistance layer is disclosed. Further, it is described that the resistance change described in non-patent document 1 occurs when the oxygen atoms gather at the vicinity of the interface between the electrode layer and the tantalum oxide layer and diffuse by the electric field.